The present invention relates to inkjet printers. More particularly, the present invention relates to a technique for encoding drop weight for a particular printhead using resistance values thereby allowing the printer to compensate for manufacturing tolerances of the printhead.
Thermal inkjet printers operate by rapidly heating a small volume of ink and causing the ink to vaporize, thereby ejecting a droplet of ink through an orifice to strike a recording medium, such as a sheet of paper. When a number of orifices are arranged in a pattern, the properly sequenced ejection of ink from an orifice causes characters or other images to be printed upon the recording media as the printhead is moved relative to the recording medium.
The printhead typically includes an orifice plate having very small nozzles through which the ink droplets are ejected. Adjacent to the nozzles inside the printhead are ink chambers, where ink is stored prior to ejection. Ink is delivered to the ink chambers through ink channels that are in fluid communication with an ink supply. The ink supply may be contained in a reservoir proximate the printhead or in the case of xe2x80x9coff-axisxe2x80x9d printers, the ink supply may be spaced from the printhead.
Ejection of an ink droplet through a nozzle may be accomplished by quickly heating a volume of ink within the ink chamber. Rapid expansion of ink vapor forces ink within the chamber through the corresponding nozzle forming a droplet. This process is called xe2x80x9cfiringxe2x80x9d. The ink in the chamber is heated with a heat transducer that is aligned with the corresponding nozzle. Typically, the heat transducer is a resistor, or piezoelectric transducer, but may comprise any substance or device capable of quickly heating the ink.
The inkjet printhead is often mounted in a print cartridge which contains some form of ink reservoir portion. In the manufacture of inkjet print cartridges and more specifically, inkjet printheads, manufacturing tolerances tend to result in variation in drop volume from one printhead to next. This drop volume variation results from manufacturing tolerances in orifice diameter, the heating element formation such as resistor size in the case of a resistive heating element, the ink chamber size, and the ink channel dimensions, to name a few. These manufacturing tolerances all tend to produce variations in ink drop volume from one printhead to the next.
Some printers use techniques such as drop counting to determine an amount of ink remaining. As a result of drop volume variation, it is difficult to determine the amount of ink remaining in the ink cartridge or external ink supply. Therefore, manufacturing tolerances resulting in drop volume variation make drop counting techniques less reliable.
In addition, this drop volume variation effects the output image quality formed on print media. The drops that are ejected onto the print media form small dots on the print media. In the case of text printing the drop volume variation tends to result in dot size variation resulting in poor dot overlap. Poor dot overlap in text images results in poor print quality. In the case of images which are formed having a varying intensities sometimes referred to as xe2x80x9cgrayscale imagesxe2x80x9d the color intensity or hue is related to the dot density. For example, in color printing frequently cyan, magenta and yellow drops of ink are used to produce a gamut of colors. Drop weight variation among different colors alters the dot size and therefore alters dot coverage which significantly affects the color reproduction. For example, if the magenta drop volume is significantly higher than intended, a hue shift will result in the output image which seriously reduces the printed image quality.
One solution is to make use of manufacturing techniques which produce tighter manufacturing tolerances. One problem associated with this technique is that these manufacturing methods which provide improved tolerances tend to be costly which tend to increase the cost of the inkjet print cartridge.
The present invention is an inkjet print cartridge for use in an inkjet printing apparatus for forming images on print media. The inkjet print cartridge includes an inkjet printhead that is responsive to print control signals for ejecting ink drops onto print media. The inkjet printhead has a manufacturing tolerance associated therewith producing a range of drop weights. The inkjet printhead has a corresponding drop weight from the range of drop weights. Included with the inkjet print cartridge is an information storage device that is associated with the inkjet printhead for storing information for identifying a corresponding drop weight from the range of drop weights.
In the preferred embodiment the inkjet print cartridge the storage device is a circuit having a resistance value corresponding to the corresponding drop weight for the printhead. In the preferred embodiment, the inkjet printing apparatus receives the inkjet print cartridge. The inkjet printing apparatus includes an information reading device for reading the drop volume information associated with the inkjet printhead. The inkjet printing apparatus makes use of the drop volume information for compensating for the manufacturing tolerance.